Bake Shop Basics: Quick Quilt Math


Oda May helps with some basic math to answer the question: How many precuts do I need?

Recently a Moda Bake Shop reader wrote in asking me a question:

What are the requirements for charm packs, layer cakes, etc to make assorted size quilts. Baby size requires how many charm packs or jelly rolls? Queen requires how many layer cakes, etc?

This is a tough question to answer on the face of it because patterns use fabric in too many ways to count, but some quick math can help us figure out the simplest of quilts that are just made up of squares sewn together.

These calculations are based on the following stats:

  • All seams measure ¼”.
  • Crib = 36” x 60”, Twin =  63” x 87”, Full =  78” x 87”, Queen = 84” x 92”, King = 106” x 98” {more bedding dimensions}
  • Precut dimensions and quantity per package are listed in our {Equivalent Measures} printable
  • Remember to use finished size for calculations

To calculate how many charm squares to make a crib quilt, let’s start with the long side:

4½” Finished Size multiplied by No. of Charm Squares = 60″

No. of Charm Squares = 60″ divided by 4½”

No. of Charm Squares = 13.333 (round up to 14 or down to 13)

Using the same process for the short side, we get 8 charm squares. So our crib sized quilt will be 8 charm squares wide by 13 charm squares tall. 8 x 13 = 104 charm squares.

Repeat the steps shown above to calculate requirements for other sizes. Moda Fabrics has a wonderful printable that shows basic setting sizes for queen quilts using various pieces. You can find that {here}.

I often contemplate how many of each precut I’d like to keep in my stash, particularly when I don’t have a project in mind but just want to keep some of the fabric on hand. I call these some-day projects “Future Quilts” and I use a simple trick to figure out how much fabric to buy without knowing which pattern I’ll be using in the future – I calculate the area! Most of us have a favorite size quilt we like to make and mine is 84″ square. It’s generous for snuggling on the sofa and works on a bed, too. This method isn’t perfect since it’s hard to account for seam allowances but it gives you a basic idea of how many you will need.

Here’s the math:

First, calculate the area of the quilt top…84″ x 84″ = 7056 in².

Second, calculate the area of the precut. I’ll use a jelly roll which measures 2½” wide x 44″ long and contains 42 strips, but we will use the finished size of 2″ x 43″.

The area of one strip is 2″ wide x 43″= 86 in²

The area of the entire jelly roll is 86 in² x 42 = 3612 in²

Area of our Future Quilt divided by Area of Jelly Roll = How Many Jelly Rolls to Buy

7056 in² divided by 3612 in² = 1.95 rounded up to 2 jelly rolls

Of course, most patterns use background fabric and borders so buy with this in mind. You can use the trick of calculating the area to substitute one of the jelly rolls or other precuts. (Area of 1 yard of quilting fabric = 1548 in² so you will need 2⅓ yards plus 1 jelly roll for the 84″ Future Quilt).

Class dismissed!

Happy Sewing,

2 comments on “Bake Shop Basics: Quick Quilt Math

  1. Thanks! I rarely buy fabrics that I already have a plan for, and nothing is more frustrating than realizing that the fabric you fell in love with and finally get ready to use, design or choose a pattern for is out of print or impossible to find and you’re short on what you need! Besides, although I am a new quilter, I never follow a pattern exact no matter what craft medium I am doing (knit,. embroidery, hand needle work, etc.) So much better to have a little (or a lot!) more and make a matching pillow, candle mat or mug rug!
    I don’t think anyone can say that they have too much Moda!

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